The present invention relates to information delivery and distribution, and more particularly, to a time division multiplexing over broadband modulation method and apparatus that enables the delivery of allocated, unshared and deterministic bandwidth to subscribers in a network.
The demand for broadband content by business and residential subscribers is continually increasing. Broadband content includes multiple types of entertainment programming, communications and data, such as broadcast television channels, video on demand, streaming video, multimedia data, internet access, voice-over-IP, etc. To meet the increasing demand, it is necessary to increase bandwidth to each subscriber and to improve quality of service. Current delivery technologies include several variations of DSL (digital subscriber line) technology, such as ADSL (asymmetrical DSL) and the like, which uses telephony technology, cable modem systems using television technology and HFC (hybrid fiber coax) distribution networks, 2-way wireless local loop (WLL), including 2-way satellite, etc. The existing legacy technology for providing broadband content is becoming increasingly inadequate to meet the demand.
DSL technology is a method of delivering data over a twisted pair of copper wires or twisted pair cables, and typically uses the Public Switched Telephone Networks (PSTN). There are several major problems with provisioning video services over the existing PSTN and twisted pair cables (network plant). The existing network plant is not uniform and most of the plant is old with poor copper conditions that cause signal loss and line noise. In fact, ADSL cannot be provisioned for a large portion of the population over the existing plant because of significant distances to the closest DSL Access Multiplexor (DSLAM) and poor conditions of the existing plants. In addition, ADSL currently has a limited downstream bandwidth, and inherently provides a very limited return bandwidth. ADSL is not adequate for many types of content originating at a subscriber destination, such as video conferencing and the like because of its bandwidth limitations and characteristics.
Cable modem systems for delivery of data services using Data-Over-Cable Service Interface Specifications (DOCSIS) utilize the television broadcast spectrum and television technology to broadcast so-called broadband data to subscribers. One problem with delivery of broadband data (video on demand, streaming video, etc.) using existing HFC networks is the limitation on available delivery spectrum. The television data delivery systems have been established to deliver data to subscribers over a television broadcast spectrum extending from approximately 15 Megahertz (MHz) to approximately 860 MHz. Delivery of analog television downstream to the subscriber occupies the spectrum between approximately 54 MHz to 550 MHz, which leaves a relatively small range of spectrum for the delivery of digital information over HFC cable modem systems. The diplex filter separating the downstream from the upstream is located within the frequency range of approximately 42 to 54 MHz in an extended sub-split frequency plan, which is common for most consumer-based HFC systems. Therefore, the two effective delivery frequency ranges using typical consumer-based HFC systems are those between approximately 15-42 MHz (upstream) and those between approximately 5 50-860 MHz (downstream).
Data-Over-Cable Service Interface Specifications (DOCSIS) is a standard that specifies the methodology for delivering data services over an HFC plant. DOCSIS defines a Cable Modem Termination System (CMTS), which is an entity used to deliver data services over an HFC network from a central distribution point. These legacy systems use a shared frequency channel to broadcast all data to every downstream subscriber. The shared channel is generally 6 MHz wide providing a total data bandwidth of approximately 27-38 megabits per second (Mbps) for digital information. The channel, however, is shared among many subscribers, so that the data rate varies dramatically depending upon the time of use and the number of subscribers simultaneously logged on. The quality of service is particularly low during popular usage time periods. An exemplary legacy system might distribute the shared channel among 4 separate nodes, each serving approximately 500 subscribers or more, so that resulting downstream data rate is often relatively low. The upstream shared channel is usually smaller, such as 3.2 MHz or less, and a xe2x80x9cpoll and grantxe2x80x9d system is employed to identify data for upstream transmission. The resulting upstream performance is often no higher (and sometimes less) than a standard 56 Kbps modem.
It is desired to provide a system and method for distributing information via existing and future communication networks that meets the increasing demand for broadband content.
A packet switch router according to embodiments of the present invention processes downstream digital information at a point of distribution to provide dedicated bandwidth for each of a plurality of subscriber destinations in a hybrid fiber coax (HFC) network. The packet switch router includes a network interface module that terminates a network connection, a switch that forwards packetized data from the network interface module, and at least one channel module. The channel module includes a switch interface, a cell processing engine, one or more modulators, and a radio frequency (RF) transmitter network. The switch interface receives and forwards packetized data from the switch to the cell processing engine. The cell processing engine forwards the packetized data into multiple data streams, encapsulates the packetized data in each data stream into data cells, and multiplexes the data cells of each the data streams into a multiplexed stream of data cells. Each modulator is configured to modulate a corresponding multiplexed stream of data cells into an analog signal. The RF transmitter network upconverts and combines a plurality of analog signals into a combined electrical signal for transmission.
A channel module in accordance with embodiments of the present invention includes an interface that receives packetized data, a cell processing engine, a modulator, and an RF transmitter network. The cell processing engine includes a switch that forwards the packetized data into one or more data streams, an encapsulator that encapsulates the packetized data in each data stream into data cells, and a channelizer that multiplexes the data cells of each data streams into a multiplexed stream of data cells. In one embodiment, the cell processing engine includes a frame processor that decapsulates the packetized data in one format and re-assembles packets into a different format. For example, the packetized data may be re-assembled back into IP packets. The cell processing engine may further include a packet adaptation procedure (PAP) processor that frames the re-assembled packets in each data stream with a frame header including a length value indicative of the size of each packet. The encapsulator may further include a cell convergence procedure (CCP) processor that generates the data cells by segmenting framed packets and encapsulating each segment with a CCP header. The CCP header includes a pointer value indicative of the location of a next frame header in a stream of data cells. In a particular embodiment, the CCP processor adds a synchronization value in accordance with MPEG-2 to spoof an MPEG data stream. The CCP processor may be configured to pad partial segments with at least one null value to create equal-sized data cells. The CCP processor may further be configured to generate null data cells if input packetized data is not available to maintain a continuous synchronous data stream.
In more particular embodiments, the channelizer operates to organize the multiplexed stream of data cells into cell groups, where each cell group includes multiple time slots. The channelizer inserts data cells from each of data stream according to assigned time slots. A memory may be included, which stores a lookup table with time slot assignments for each data stream. In a particular embodiment, the lookup table maps timeslots to destination IP addresses corresponding to each data stream, where the destination IP addresses each correspond to a subscriber destination. The modulator may include an encoder or the like that adds redundant data to each data cell prior to transmission to enable the receiver to reconstruct data cells in the event of lost or erroneous data. In such configuration, the cell processing engine may be configured to insert a delay between each data cell of the multiplexed stream of data cells while transmitting to the modulator to maintain timing between the cell processing engine and the modulator. In one embodiment, the modulator includes a randomizer, an encoder, and a quadrature amplitude modulator (QAM). A QAM-256 modulator is contemplated to achieve high data throughput in the downstream direction. The encoder may be a Reed-Solomon encoder or the like. Several multiplexed data cell streams are contemplated depending upon the particular data throughput that is desired. In multiple data stream configurations, the cell processing engine outputs more than one multiplexed data cell stream, each provided to a corresponding modulator. The RF transmitter network includes a combiner that combines multiple frequency channels into a single electrical signal.
It is appreciated that each data stream may correspond to one of multiple downstream subscriber destinations. The process of converting each data stream into a stream of cells enables multiplexing the cells from multiple data streams. This results in a single multiplexed data stream that is used to service multiple subscribers. Furthermore, dividing the stream into cell groups, each group having a fixed number of time slots or transport channels, enables each subscriber to have a dedicated downstream bandwidth. For example, in a particular embodiment employing 6 MHz channels and QAM-256 modulation, each frequency channel is capable of supporting approximately 40 Mbps data throughput. Time division multiplexing or time slot channelization of the frequency channel allows the 40 Mbps throughput to be further sub-divided. For example, organizing the cell stream into eight different transport channels allows each transport channel to support approximately 5 Mbps. Thus, eight different subscriber destinations may each be allocated a dedicated channel having 5 Mbps bandwidth. Of course, a given subscriber destination may be allocated multiple time slots to achieve an incremental increase in the dedicated bandwidth to that subscriber. For example, 3 of 8 transport channels assigned to a single subscriber destination provides approximately 15 Mbps to that subscriber destination.
A method of processing digital information by a point of distribution in accordance with embodiments of the present invention provides dedicated bandwidth to multiple subscriber destinations via an HFC network. The method includes forwarding data packets into multiple data streams, framing each data packet in each data stream, segmenting encapsulated data packets into data segments, encapsulating data segments of each data stream into data cells to form a corresponding cell streams, multiplexing the cell streams into a multiplexed cell stream, and modulating the multiplexed cell stream into a modulated signal within a frequency channel. The method may further include receiving and processing digital information into data packet information. The method may further include assembling the data packet information into data packets.
The framing may include appending a packet header including a length value indicative of the size of the data packet. The segmenting may include incorporating the packet header in a first segment for each segmented data packet. The encapsulating data segments may include appending a cell header to each data segment, where the cell header includes an offset value indicating a beginning of a next segmented data packet in the multiplexed cell stream. The encapsulating may include adding a synchronization value in accordance with the MPEG-2 format, which is particularly advantageous in that off-the-shelf components may be used to reduce cost and development time. The method may further include verifying that each offset value is compatible with a length value for a corresponding segmented data packet. The cell header may include a synchronization value to enable synchronization with the downstream subscriber destination equipment. The encapsulating may further include padding incomplete data cells with null values to achieve equal-sized data cells in the multiplexed cell stream. The multiplexing may include inserting data cells from each cell stream into the multiplexed cell stream in a round-robin manner.
In a more particular embodiment, the multiplexing may include organizing the multiplexed cell stream into cell groups, where each cell group has an equal number of time slots, and inserting data cells from each cell stream into the time slots of each cell group. The method may further include assigning at least one time slot of the cell group to each data stream, and inserting data cells from each cell stream into assigned time slots. The method may further include sending the multiplexed cell stream as a synchronous cell stream to a modulator.
After multiplexing and before modulating, the method may include modifying periodic synchronization values within cell headers that are appended to each data cell, scrambling a payload of each data cell within the multiplexed cell stream, and encoding data cells in the multiplexed cell stream. The encoding may be according to any suitable encoding scheme, such as according to Reed-Solomon or the like. The modulation may be according to any known or later developed modulation techniques, such as quadrature amplitude modulation (QAM) or the like as previously described.
The multiplexing may include multiplexing the cell streams into multiple cell streams, each multiplexed in a similar manner. Modulating is performed on each multiplexed cell stream to achieve a corresponding modulated signal within a corresponding one of multiple frequency channels. The method may further include combining the frequency channels into a single electrical signal. The method may include converting the electrical signal into an optical signal for transmission to an optical node.
A method of providing dedicated bandwidth to each of multiple subscriber destinations for delivering source information over an HFC network is similar to the method describe above, and includes modulating a multiplexed cell stream into an analog signal in a frequency channel, converting the analog signal to an optical signal, and transmitting the optical signal to the subscriber destinations over the HFC network. The method may further include receiving data packets at a distribution hub, decapsulating the data packets to obtain IP packet data, and re-assembling the IP packet data into IP packets. The method may further include receiving an optical signal from a headend and converting the optical signal into the data packets. The forwarding digital information may include determining digital addresses associated with the subscriber destinations. The method may include converting the digital information into data packets, segmenting the data packets in each data stream into packet segments, framing the packet segments with frame headers, and encapsulating framed packet segments into the data cells, where each data cell includes a cell header. The method may further include transmitting the optical signal to an optical node, converting, by the optical node, the optical signal to an electrical signal, and transmitting the electrical signal from the optical node to the subscriber destinations via a coaxial cable.